The present invention relates generally to combine harvesters and, more particularly, to a method for utilizing a rotary cleaning mechanism in combines for cleaning unwanted residue, such as chaff, straw, etc., from threshed grain.
Conventional cleaning systems clean threshed grain by blowing air through a set of planar sieves utilizing gravitational forces to urge cleaned grain through the sieve openings. With the advent of higher capacity threshing and separating mechanisms, such as rotary axial flow combines, the capacity for threshing grain has increased beyond the capacity of conventional cleaning systems to clean the grain. Accordingly, it is desirable to increase both the capacity and the efficiency of cleaning systems in combine harvesters so as not to limit the throughput capability of the combine.
The utilization of centrifugal forces to urge grain through the sieve openings, rather than gravitational forces, will increase the capacity of the cleaning system. The provision of axially extending cleaning shoes reciprocatably moving along a slightly non-axial direction directed inwardly toward the axis of rotation permits a sleek, efficient cleaning device to be incorporated in the base unit of the combine. The use of a blowing fan, as compared to a fan that draws air through the cleaning cylinder, enables the flow of air to be directed in an efficient manner.